Field of the Invention
The invention relates to a chip card having a semiconductor chip that contains at least one memory, contacts and a device for contactless data transmission for supplying energy to the chip and for bi-directional data transmission from and to the chip, and a triggerable switch device disposed on the chip for connecting the memory either to the contacts or to the device for contactless data transmission, depending on a state of an output signal of a logic circuit connected to at least a voltage supply contact.
One such chip card is already known from Published European Patent Application 0 424 726 A1. In that device, the logic circuit is constructed as a comparator having one input which is connected to the supply voltage contact. The other input of the comparator is connected, through a rectifier and smoothing network, to coils for contactless energy and data transmission. An output of the comparator operates as a function of voltages applied to its two inputs to trigger a multiplexer which operates as a function of the status of the output signal of the comparator to switch either the supply voltage and the signals of the contacts, or the supply voltage and the signals that have been derived from the signal received by the coils, to a microprocessor that is also connected to the multiplexer and has an associated memory.
Accordingly, in the known chip card, an automatic switchover to either the contacts or the coils is possible, depending on where the chip card has received its supply voltage from. However, one disadvantage of that device is that the memory is always connected to an input/output interface which furnishes the higher supply voltage. As a result, even if the chip card was inserted into a conventional card reader that has contacts, the multiplexer could be switched over by the application of a strong electromagnetic field, thus making misuse of the card possible. That is a problem, above all because in such combined cards, in which energy and data transmission can be carried out either through contacts or contactlessly through coils, and where those cards are used as debit cards, debiting of the card is normally carried out through the contactless transmission route, while incrementing the value of the card is carried out through the conventional transmission route, with contacts. That provides an inducement to swindlers to manipulate the card while it is inserted in a conventional card reader for charging.